Display screen or portion thereof with a transitional graphical user interface



1. Display screen or portion thereof with a transitional graphical user interface

1.1 : Front

1.2 : Front

1.3 : Front

1.4 : Front

1.5 : Front

1.6 : Front

1.7 : Front

The broken line display screen as well as the broken lines showing portions of the transitional graphical user interface are included for illustrative purposes only and form no part of the claimed design.

The appearance of the transitional image sequentially transitions between the images shown in figs. 1.1 - 1.7 . The process or period in which one image transitions to another image forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a transitional graphical user interface, as shown and described. 